As set out, for example, in Patent Document 1 indicated below, a hydraulic control apparatus for a continuously variable transmission equipped with a drive pulley connected to an engine mounted in a vehicle, a driven pulley connected to driven wheels and a belt wound around the pulleys is ordinarily operated by supplying hydraulic oil from a hydraulic pump driven by the engine to hydraulic actuators of the drive pulley and driven pulley.
Regarding the hydraulic pump driven by the engine, Patent Document 2 indicated below teaches a technique for establishing characteristics capable of ensuring the required hydraulic pressure under all conditions, which, with concern about low energy efficiency, installs two servo pumps driven by electric motors, and uses the state variable of a state variable model of a servo pump system whose input is a quantity of state having a linear relationship to the voltage input to servo amplifiers of the electric motors so as to perform state feedback control for regulating the hydraulic oil flow rate to the desired flow rate.
Further, in a similar servo pump system, Patent Document 3 indicated below teaches a technique of combining a feedback linearization unit linearized by an input/output feedback linearization with a plant whose input is the hydraulic oil flow rates to the hydraulic actuators and output is the resulting drive pulley and driven pulley pressures, wherein input to the feedback linearization unit is controlled based on deviation between the pressures output from the plant and the desired pressures.